1. Field of the Invention
The present invention relates to a projector device, having a photographing function capable of photographing and recording projected contents, a method of photographing a projected image, and a program.
2. Description of the Related Art
In recent years, with spread of personal computers, portable projector devices have been more familiar which can perform various types of presentations, demonstrations and the like, when connected to notebook or handheld types of personal computers.
As this type of projector device, there are: a device in which a transmission type of color liquid crystal panel is used as an element to form an optical image; and a device of a digital light processing (DLP) (registered trademark) system in which an optical semiconductor device referred to as a micromirror element is used.
In the projector device of the DLP (registered trademark) system, a disc-shaped member referred to as a color wheel in which color filters (segments) of red, green, blue, and white are dividedly arranged on the same circumference is driven and rotated to color high-luminance white light from a light source lamp in time division (precisely, the only light of a corresponding color component is selectively transmitted). Thereafter, the light is reflected by a micromirror element driven and displayed to form the optical image corresponding to the color component, and the reflected light is projected on a screen or the like which is a projection object via a lens of an optical projection system.
Moreover, especially even in a projector device using a liquid crystal display panel referred to as a field sequential system, a basic concept closely resembles that of the projector device of the above-described DLP (registered trademark) system in that a light source lamp of three colors R, G, B is driven and lit in time division, and the image corresponding to the color component is displayed in a monochromatic liquid crystal display panel in each lighting period.
Therefore, there is also a need to record the image projected as described above in a digital camera separately prepared, for example, in making minutes. However, in the above-described projector device which is driven in time division for each color component constituting the image, there is a high possibility that an image having a large color unbalance is recorded depending on a photographing timing.
FIG. 6 shows a rotated state of the color wheel and the photographing timing in the general projector device of the DLP (registered trademark) system. In the figure, a frame frequency of an input image signal is 60 Hz, and the frequency is further divided into two in order to suppress flickering of the image so that the same image is projected and displayed twice at 120 Hz.
FIG. 6(1) shows a vertically synchronous signal synchronized with the input image signal, and FIG. 6(2) shows the segments of the color wheel which is driven and rotated in synchronization with the signal and which is inserted into an optical projection axis from the light source lamp.
It is now assumed that a shutter button of a digital camera is operated to photograph the projected image at a timing shown in FIG. 6(3), and thereafter the photographing is executed with a time lag as much as a time for each processing of autofocusing (AF) and automatic exposure (AE).
FIG. 6(4) shows a photographing timing (=exposure timing in which a mechanical shutter of the digital camera is actually opened) in a case where the image is photographed at a shutter speed which is sufficiently higher than one frame period of 1/120 second. Naturally, the timing is not synchronized with the rotated state of the color wheel. This timing centers on the green (G) segment of the color wheel which is disposed in the optical projection axis, and the photographing is executed ranging from a part of the previous red (R) segment to a part of the subsequent blue (B) segment.
In this case, the image obtained by the photographing is an entirely greenish image, because an exposure time of the image of a green (G) component is longer than that of the image of each of red (R) and blue (B) components.
FIG. 6(5) shows a photographing timing in a case where a focal number (F) is set to be large, and the shutter speed is set to be low in order to avoid the above-described situation. In this case, when the shutter speed is set to a low speed, for example, of 1/15 or 1/30 second, the exposure time is sufficiently long as compared with a rotation period of the color wheel. Therefore, the photographed image does not have unbalanced color components and is not unnatural. However, the image is easily influenced by hands movement. Moreover, there is a high possibility of an overexposure depending on brightness of the projected and displayed image.
The present invention has been developed in view of the above-described situations, and an object is to provide a projector device which is of such a system as to perform time-division projecting and driving for each of a plurality of color components of a color image and which can securely photograph a projected image having a satisfactory color balance, and a method and a program for photographing a projected image.